The production of hydrocarbons from geological stratum is an important part of modern economic development. Many different types of tools may be used to identify and retrieve these hydrocarbon materials from the geological stratum. Devices range from simple mechanical tools, such as drill bits, drill pipe and derricks to more complicated devices, such as nuclear magnetic resonance tools.
The more complex the tool, generally, the more potential sources of problems may be encountered. For some of the most complex tools, such as nuclear magnetic resonance tools, the complex machinery and devices that are used make the device prone to erroneous readings.
For nuclear magnetic resonance tools, different signals may be received by the circuitry and sensors or may be present or induced in the tool that may make the tool prone to erroneous readings. Typically, nuclear magnetic resonance tools require a conductive shield around the antenna to eliminate electromagnetic noise from environment, for example, to make accurate calibration measurements. Eddy currents induced in the shield boost the magnetic field created by the tool at the diameter of investigation. This, in turn, increases the nuclear magnetic resonance signal of the tool during the calibration measurements. The above-described shield effect introduces an error during the calibration measurements and thus degrades the desired porosity measurement accuracy if not properly corrected. One way to reduce to the shield eddy current effect is to use a really big 8′ long shield. This big shield occupies a lot of space in the lab.